Detection of and counter-measures for jackknife enabling conditions during trailer backup assist

ABSTRACT

A vehicle comprises a trailer angle detection apparatus and a trailer backup control system coupled to the trailer angle detection apparatus. The trailer angle detection apparatus is configured for outputting a signal generated as a function of an angle between the vehicle and a trailer towably attached to the vehicle. The trailer backup control system includes a jackknife enabling condition detector and a jackknife counter-measures controller. The jackknife counter-measures controller alters a setting of at least one vehicle operating parameter for alleviating an adverse jackknife condition during backing of the trailer by the vehicle when the jackknife enabling condition detector determines that a jackknife enabling condition has been attained at a particular point in time during backing of the trailer by the vehicle.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of co-pending U.S. applicationSer. No. 13/443,743, which was filed on Apr. 10, 2012, which is entitled“Detection Of And Counter-Measures For Jackknife Enabling ConditionsDuring Trailer Backup Assist”, which is a continuation-in-partapplication of U.S. Non-provisional patent application which has Ser.No. 13/336,060, filed Dec. 23, 2011, entitled “Trailer Path CurvatureControl For Trailer Backup Assist”, which claims priority from U.S.Provisional Patent Application which has Ser. No. 61/477,132, filed Apr.19, 2011, entitled “Trailer Backup Assist Curvature Control”, and bothof which have a common applicant herewith and are being incorporatedherein in their entirety by reference.

FIELD OF THE DISCLOSURE

The disclosures made herein relate generally to driver assist and activesafety technologies in vehicles and, more particularly, to implementingjackknife detection and counter-measures during back-up of a trailer.

BACKGROUND

It is well known that backing up a vehicle with a trailer attached is adifficult task for many drivers. This is particularly true for driverswho are untrained at backing with trailers such as, for example, thosewho drive with an attached trailer on an infrequent basis (e.g., haverented a trailer, use a personal trailer on an infrequent basis, etc).One reason for such difficulty is that backing a vehicle with anattached trailer requires counter-steering that is opposite to normalsteering when backing the vehicle without a trailer attached and/orrequires braking to stabilize the vehicle-trailer combination before ajack-knife condition occurs. Another reason for such difficulty is thatsmall errors in steering while backing a vehicle with an attachedtrailer are amplified, thereby causing the trailer to depart from adesired path.

To assist the driver in steering a vehicle with trailer attached, atrailer backup assist system needs to know the driver's intention. Onecommon assumption with known trailer backup assist systems is that adriver of a vehicle with an attached trailer wants to back up straightand the system either implicitly or explicitly assumes a zero curvaturepath for the vehicle-trailer combination. Unfortunately most ofreal-world use cases of backing a trailer involve a curved path and,thus, assuming a path of zero curvature would significantly limitusefulness of the system. Some known systems assume that a path is knownfrom a map or path planner. To this end, some known trailer backupassist systems operate under a requirement that a trailer back-up pathis known before backing of the trailer commences such as, for example,from a map or a path planning algorithm. Undesirably, suchimplementations of the trailer backup assist systems are known to have arelatively complex Human Machine Interface (HMI) to specify the path,obstacles and/or goal of the backup maneuver. Furthermore, such systemsalso require some way to determine how well the desired path is beingfollowed and to know when the desired goal, or stopping point andorientation, has been met, using approaches such as cameras, inertialnavigation, or high precision GPS. These requirements lead to arelatively complex and costly system.

As previously mentioned, one reason backing a trailer can prove to bedifficult is the need to control the vehicle in a manner that limits thepotential for a jack-knife condition to occur. A trailer has attained ajackknife condition when a hitch angle cannot be reduced (i.e., madeless acute) by application of a maximum steering input for the vehiclesuch as, for example, by moving steered front wheels of the vehicle to amaximum steered angle at a maximum rate of steering angle change. In thecase of the jackknife angle being achieved, the vehicle must be pulledforward to relieve the hitch angle in order to eliminate the jackknifecondition and, thus, allow the hitch angle to be controlled viamanipulation of the steered wheels of the vehicle. However, in additionto the jackknife condition creating the inconvenient situation where thevehicle must be pulled forward, it can also lead to damage to thevehicle and/or trailer if certain operating conditions of the vehiclerelating to its speed, engine torque, acceleration, and the like are notdetected and counteracted. For example, if the vehicle is travelling ata suitably high speed and/or subjected to a suitably high longitudinalacceleration when the jackknife condition is achieved, the relativemovement of the vehicle with respect to the trailer can lead to contactbetween the vehicle and trailer thereby damaging the trailer and/or thevehicle.

Therefore, an approach for detecting an actual or impending jackknifecondition (i.e., a jackknife enabling condition) and correspondinglyimplementing a jackknife counter-measure and, optionally, a jackknifewarning would be beneficial, desirable and useful.

SUMMARY OF THE DISCLOSURE

Embodiments of the inventive subject matter are directed to assisting adriver with backing a trailer attached to a vehicle in a manner thatlimits the potential for a jackknife condition being attained betweenthe vehicle and the trailer. More specifically, embodiments of theinventive subject matter are directed to detecting an impendingjackknife condition (i.e., a jackknife enabling condition) andcorrespondingly implementing a jackknife counter-measure for alleviatingthe impending jackknife condition. Optionally, in some embodiments ofthe inventive subject matter, a warning (e.g., tactile, audible, visualand/or the like) can be implemented in response to an impending and/oractual jackknife condition being detected. Accordingly, embodiments ofthe inventive subject matter contribute to trailer backup assistfunctionality being implemented in a manner that is relatively simple,effective, and safe.

In one embodiment of the inventive subject matter, a method comprisesassessing jackknife determining information for a vehicle and a trailertowably to the vehicle and, in response to the jackknife determininginformation indicating that a jackknife enabling condition has beenattained at a particular point in time during backing of the trailer bythe vehicle, implementing a jackknife counter-measure. Implementing thejackknife counter-measure includes altering at least one vehicleoperating parameter upon which the jackknife enabling condition isdependent.

In another embodiment of the inventive subject matter, a vehiclecomprises a trailer angle detection apparatus and a trailer backupcontrol system coupled to the trailer angle detection apparatus. Thetrailer angle detection apparatus is configured for outputting a signalgenerated as a function of an angle between the vehicle and a trailertowably attached to the vehicle. The trailer backup control systemincludes a jackknife enabling condition detector and a jackknifecounter-measures controller. The jackknife counter-measures controlleralters a setting of at least one vehicle operating parameter foralleviating an adverse jackknife condition during backing of the trailerby the vehicle when the jackknife enabling condition detector determinesthat a jackknife enabling condition has been attained at a particularpoint in time during backing of the trailer by the vehicle.

In another embodiment of the inventive subject matter, an electroniccontrol system has a set of instructions tangibly embodied on anon-transitory processor-readable medium thereof. The set ofinstructions are accessible from the non-transitory processor-readablemedium by at least one data processing device of the electroniccontroller system for being interpreted thereby. The set of instructionsis configured for causing at least one data processing device to carryout operations for assessing jackknife determining information for avehicle and a trailer towably attached to the vehicle and, in responseto the jackknife determining information indicating that a jackknifeenabling condition has been attained at a particular point in timeduring backing of the trailer by the vehicle, for implementing ajackknife counter-measure. Implementing the jackknife counter-measureincludes altering at least one vehicle operating parameter upon whichthe jackknife enabling condition is dependent.

These and other objects, embodiments, advantages and/or distinctions ofthe inventive subject matter will become readily apparent upon furtherreview of the following specification, associated drawings and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a vehicle configured for performing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter embodiment.

FIG. 2 shows a preferred embodiment of the trailer backup steering inputapparatus discussed in reference to FIG. 1.

FIG. 3 shows an example of a trailer backup sequence implemented usingthe trailer backup steering input apparatus discussed in reference toFIG. 2.

FIG. 4 shows a method for implementing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter.

FIG. 5 is a diagrammatic view showing a kinematic model configured forproviding information utilized in providing trailer backup assistfunctionality in accordance with the inventive subject matter.

FIG. 6 is a graph showing an example of a trailer path curvaturefunction plot for a rotary-type trailer backup steering input apparatusconfigured in accordance with the inventive subject matter.

FIG. 7 is a diagrammatic view showing a relationship between hitch angleand steered angle as it relates to determining a jackknife angle for avehicle/trailer system.

FIG. 8 shows a method for implementing jackknife countermeasuresfunctionality in accordance with an embodiment of the inventive subjectmatter.

DETAILED DESCRIPTION OF THE DRAWING FIGURES

The inventive subject matter is directed to providing trailer backupassist functionality. In particular, such trailer backup assistfunctionality is directed to implementing one or more countermeasuresfor limiting the potential of a jackknife condition being attainedbetween a vehicle and a trailer being towed by the vehicle. In certainembodiments of the inventive subject matter, curvature of a path oftravel of the trailer (i.e., trailer path curvature control) can becontrolled by allowing a driver of the vehicle to specify a desired pathof the trailer by inputting a desired trailer path curvature as thebackup maneuver of the vehicle and trailer progresses. Although acontrol knob, a set of virtual buttons, or a touch screen can each beimplemented for enabling trailer path curvature control, the inventivesubject matter is not unnecessarily limited to any particularconfiguration of interface through which a desired trailer pathcurvature is inputted. Furthermore, in the case where a steering wheelcan be mechanically decoupled from steered wheels of the vehicle, thesteering wheel can also be used as an interface through which a desiredtrailer path curvature is inputted. As will be discussed herein ingreater detail, kinematical information of a system defined by thevehicle and the trailer are used to calculate a relationship (i.e.,kinematics) between the trailer's curvature and the steering angle ofthe vehicle for determining steering angle changes of the vehicle forachieving the specified trailer path. Steering commands corresponding tothe steering angle changes are used for controlling a steering system ofthe vehicle (e.g., electric power assisted steering (EPAS) system) ofthe vehicle for implementing steering angle changes of steered wheels ofthe vehicle to achieve (e.g., to approximate) the specified path oftravel of the trailer.

Referring to FIG. 1, an embodiment of a vehicle 100 configured forperforming trailer backup assist functionality in accordance with theinventive subject matter is shown. A trailer backup assist system 105 ofthe vehicle 100 controls the curvature of path of travel of the trailer110 that is attached to the vehicle 100. Such control is accomplishedthrough interaction of a power assisted steering system 115 of thevehicle 100 and the trailer backup assist system 105. During operationof the trailer backup assist system 105 while the vehicle 100 is beingreversed, a driver of the vehicle 100 is sometimes limited in the mannerin which he/she can make steering inputs via a steering wheel of thevehicle 100. This is because in certain vehicles the trailer backupassist system 105 is in control of the power assisted steering system115 and the power assisted steering system 115 is directly coupled tothe steering wheel (i.e., the steering wheel of the vehicle 100 moves inconcert with steered wheels of the vehicle 100). As is discussed belowin greater detail, a human machine interface (HMI) of the backup assistsystem 105 is used for commanding changes in curvature of a path of thetrailer 110 such as a knob, thereby decoupling such commands from beingmade at the steering wheel of the vehicle 100. However, some vehiclesconfigured to provide trailer backup assist functionality in accordancewith the inventive subject matter will have the capability toselectively decouple steering movement from movement of steerable wheelsof the vehicle, thereby allowing the steering wheel to be used forcommanding changes in curvature of a path of a trailer during suchtrailer backup assist.

The trailer backup assist system 105 includes a trailer backup assistcontrol module 120, a trailer backup steering input apparatus 125, and ahitch angle detecting apparatus 130. The trailer backup assist controlmodule 120 is connected to the trailer backup steering input apparatus125 and the hitch angle detecting apparatus 130 for allowingcommunication of information there between. It is disclosed herein thatthe trailer backup steering input apparatus can be coupled to thetrailer backup assist control module 120 in a wired or wireless manner.The trailer backup assist system control module 120 is attached to apower-steering assist control module 135 of the power-steering assistsystem 115 for allowing information to be communicated therebetween. Asteering angle detecting apparatus 140 of the power-steering assistsystem 115 is connected to the power-steering assist control module 125for providing information thereto. The trailer backup assist system isalso attached to a brake system control module 145 and a powertraincontrol module 150 for allowing communication of informationtherebetween. Jointly, the trailer backup assist system 105, thepower-steering assist system 115, the brake system control module 145,the powertrain control module 150 define a trailer backup assistarchitecture configured in accordance with an embodiment of theinventive subject matter.

The trailer backup assist control module 120 is configured forimplementing logic (i.e., instructions) for receiving information fromthe trailer backup steering input apparatus 125, the hitch angledetecting apparatus 130, the power-steering assist control module 135,the brake system control module 145, and the powertrain control module150. The trailer backup assist control module 120 (e.g., a trailercurvature algorithm thereof) generates vehicle steering information as afunction of all or a portion of the information received from thetrailer backup steering input apparatus 125, the hitch angle detectingapparatus 130, the power-steering assist control module 135, the brakesystem control module 145, and the powertrain control module 150.Thereafter, the vehicle steering information is provided to thepower-steering assist control module 135 for affecting steering of thevehicle 100 by the power-steering assist system 115 to achieve acommanded path of travel for the trailer 110.

The trailer backup steering input apparatus 125 provides the trailerbackup assist control module 120 with information defining the commandedpath of travel of the trailer 110 to the trailer backup assist controlmodule 120 (i.e., trailer steering information). The trailer steeringinformation can include information relating to a commanded change inthe path of travel (e.g., a change in radius of path curvature) andinformation relating to an indication that the trailer is to travelalong a path defined by a longitudinal centerline axis of the trailer(i.e., along a substantially straight path of travel). As will bediscussed below in detail, the trailer backup steering input apparatus125 preferably includes a rotational control input device for allowing adriver of the vehicle 100 to interface with the trailer backup steeringinput apparatus 125 to command desired trailer steering actions (e.g.,commanding a desired change in radius of the path of travel of thetrailer and/or commanding that the trailer travel along a substantiallystraight path of travel as defined by a longitudinal centerline axis ofthe trailer). In a preferred embodiment, the rotational control inputdevice is a knob rotatable about a rotational axis extending through atop surface/face of the knob. In other embodiments, the rotationalcontrol input device is a knob rotatable about a rotational axisextending substantially parallel to a top surface/face of the knob.

Some vehicles (e.g., those with active front steer) have apower-steering assist system configuration that allows a steering wheelto be decoupled from movement of the steered wheels of such a vehicle.Accordingly, the steering wheel can be rotated independent of the mannerin which the power-steering assist system of the vehicle controls thesteered wheels (e.g., as commanded by vehicle steering informationprovided by a power-steering assist system control module from a trailerbackup assist system control module configured in accordance with anembodiment of the inventive subject matter). As such, in these types ofvehicles where the steering wheel can be selectively decoupled from thesteered wheels to allow independent operation thereof, trailer steeringinformation of a trailer backup assist system configured in accordancewith the inventive subject matter can be provided through rotation ofthe steering wheel. Accordingly, it is disclosed herein that in certainembodiments of the inventive subject matter, the steering wheel is anembodiment of a rotational control input device in the context of theinventive subject matter. In such embodiments, the steering wheel wouldbe biased (e.g., by an apparatus that is selectivelyengagable/activatable) to an at-rest position between opposingrotational ranges of motion.

The hitch angle detecting apparatus 130, which operates in conjunctionwith a hitch angle detection component 155 of the trailer 110, providesthe trailer backup assist control module 120 with information relatingto an angle between the vehicle 100 and the trailer 110 (i.e., hitchangle information). In a preferred embodiment, the hitch angle detectingapparatus 130 is a camera-based apparatus such as, for example, anexisting rear view camera of the vehicle 100 that images (i.e., visuallymonitors) a target (i.e., the hitch angle detection component 155)attached the trailer 110 as the trailer 110 is being backed by thevehicle 100. Preferably, but not necessarily, the hitch angle detectioncomponent 155 is a dedicated component (e.g., an item attachedto/integral with a surface of the trailer 110 for the express purpose ofbeing recognized by the hitch angle detecting apparatus 130).Alternatively, the hitch angle detecting apparatus 130 can be a devicethat is physically mounted on a hitch component of the vehicle 100and/or a mating hitch component of the trailer 110 for determining anangle between centerline longitudinal axes of the vehicle 100 and thetrailer 110. The hitch angle detecting apparatus 130 can be configuredfor detecting a jackknife enabling condition and/or related information(e.g., when a hitch angle threshold has been met).

The power-steering assist control module 135 provides the trailer backupassist control module 120 with information relating to a rotationalposition (e.g., angle) of the steering wheel angle and/or a rotationalposition (e.g., turning angle(s)) of steered wheels of the vehicle 100.In certain embodiments of the inventive subject matter, the trailerbackup assist control module 120 can be an integrated component of thepower steering assist system 115. For example, the power-steering assistcontrol module 135 can include a trailer back-up assist algorithm forgenerating vehicle steering information as a function of all or aportion of information received from the trailer backup steering inputapparatus 125, the hitch angle detecting apparatus 130, thepower-steering assist control module 135, the brake system controlmodule 145, and the powertrain control module 150.

The brake system control module 145 provides the trailer backup assistcontrol module 120 with information relating to vehicle speed. Suchvehicle speed information can be determined from individual wheel speedsas monitored by the brake system control module 145. In some instances,individual wheel speeds can also be used to determine a vehicle yawangle and/or yaw angle rate and such yaw angle and/or yaw angle rate canbe provided to the trailer backup assist control module 120 for use indetermining the vehicle steering information. In certain embodiments,the trailer backup assist control module 120 can provide vehicle brakinginformation to the brake system control module 145 for allowing thetrailer backup assist control module 120 to control braking of thevehicle 100 during backing of the trailer 110. For example, using thetrailer backup assist control module 120 to regulate speed of thevehicle 100 during backing of the trailer 1110 can reduce the potentialfor unacceptable trailer backup conditions. Examples of unacceptabletrailer backup conditions include, but are not limited to, a vehicleoverspeed condition, trailer angle dynamic instability, a trailerjack-knife condition as defined by an angular displacement limitrelative to the vehicle 100 and the trailer 110, and the like. It isdisclosed herein that the backup assist control module 120 can issue asignal corresponding to a notification (e.g., a warning) of an actual,impending, and/or anticipated unacceptable trailer backup condition.

The powertrain control module 150 interacts with the trailer backupassist control module 120 for regulating speed and acceleration of thevehicle 100 during backing of the trailer 110. As mentioned above,regulation of the speed of the vehicle 100 is necessary to limit thepotential for unacceptable trailer backup conditions such as, forexample, jack-knifing and trailer angle dynamic instability. Similar tohigh-speed considerations as they relate to unacceptable trailer backupconditions, high acceleration can also lead to such unacceptable trailerbackup conditions.

Referring now to FIG. 2, a preferred embodiment of the trailer backupsteering input apparatus 125 discussed in reference to FIG. 1 is shown.A rotatable control element in the form of a knob 170 is coupled to amovement sensing device 175. The knob 170 is biased (e.g., by a springreturn) to an at-rest position P(AR) between opposing rotational rangesof motion R(R). R(L). A first one of the opposing rotational ranges ofmotion R(R) is substantially equal to a second one of the opposingrotational ranges of motion R(L), R(R). To provide a tactile indicationof an amount of rotation of the knob 170, a force that biases the knob170 toward the at-rest position P(AR) can increase (e.g., non-linearly)as a function of the amount of rotation of the knob 170 with respect tothe at-rest position P(AR). Additionally, the knob 170 can be configuredwith position indicating detents such that the driver can positivelyfeel the at-rest position P(AR) and feel the ends of the opposingrotational ranges of motion R(L), R(R) approaching (e.g., soft endstops).

The movement sensing device 175 is configured for sensing movement ofthe knob 170 and outputting a corresponding signal (i.e. movementsensing device signal) to the trailer assist backup input apparatus 125shown in FIG. 1. The movement sensing device signal is generated as afunction of an amount of rotation of the knob 170 with respect to theat-rest position P(AR), a rate movement of the knob 170, and/or adirection of movement of the knob 170 with respect to the at-restposition P(AR). As will be discussed below in greater detail, theat-rest position P(AR) of the knob 170 corresponds to a movement sensingdevice signal indicating that the vehicle 100 should be steered suchthat the trailer 100 is backed along a substantially straight path asdefined by a centerline longitudinal axis of the trailer 110 when theknob 170 was returned to the at-rest position P(AR) and a maximumclockwise and anti-clockwise position of the knob 170 (i.e., limits ofthe opposing rotational ranges of motion R(R), R(L)) each corresponds toa respective movement sensing device signal indicating a tightest radiusof curvature (i.e., most acute trajectory) of a path of travel of thetrailer 110 that is possible without the corresponding vehicle steeringinformation causing a jack-knife condition. In this regard, the at-restposition P(AR) is a zero curvature commanding position with respect tothe opposing rotational ranges of motion R(R), R(L). It is disclosedherein that a ratio of a commanded curvature of a path of a trailer(e.g., radius of a trailer trajectory) and a corresponding amount ofrotation of the knob can vary (e.g., non-linearly) over each one of theopposing rotational ranges of motion R(L), R(R) of the knob 170. It isalso disclosed therein that the ratio can be a function of vehiclespeed, trailer geometry, vehicle geometry, hitch geometry and/or trailerload.

Use of the knob 170 decouples trailer steering inputs from being made ata steering wheel of the vehicle 100. In use, as a driver of the vehicle100 backs the trailer 110, the driver can turn the knob 170 to dictate acurvature of a path of the trailer 110 to follow and returns the knob170 to the at-rest position P(AR) for causing the trailer 110 to bebacked along a straight line. Accordingly, in embodiments of trailerbackup assist systems where the steering wheel remains physicallycoupled to the steerable wheels of a vehicle during backup of anattached trailer, a rotatable control element configured in accordancewith the inventive subject matter (e.g., the knob 170) provides a simpleand user-friendly means of allowing a driver of a vehicle to inputtrailer steering commands.

It is disclosed herein that a rotational control input device configuredin accordance with embodiments of the inventive subject matter (e.g.,the knob 170 and associated movement sensing device) can omit a meansfor being biased to an at-rest position between opposing rotationalranges of motion. Lack of such biasing allows a current rotationalposition of the rotational control input device to be maintained untilthe rotational control input device is manually moved to a differentposition. Preferably, but not necessarily, when such biasing is omitted,a means is provided for indicating that the rotational control inputdevice is positioned in a zero curvature commanding position (e.g., atthe same position as the at-rest position in embodiments where therotational control input device is biased). Examples of means forindicating that the rotational control input device is positioned in thezero curvature commanding position include, but are not limited to, adetent that the rotational control input device engages when in the zerocurvature commanding position, a visual marking indicating that therotational control input device is in the zero curvature commandingposition, an active vibratory signal indicating that the rotationalcontrol input device is in or approaching the zero curvature commandingposition, an audible message indicating that the rotational controlinput device is approaching the zero curvature commanding position, andthe like.

It is also disclosed herein that embodiments of the inventive subjectmatter can be configured with a control input device that is notrotational (i.e., a non-rotational control input device). Similar to arotational control input device configured in accordance withembodiments of the inventive subject matter (e.g., the knob 170 andassociated movement sensing device), such a non-rotational control inputdevice is configured to selectively provide a signal causing a trailerto follow a path of travel segment that is substantially straight and toselectively provide a signal causing the trailer to follow a path oftravel segment that is substantially curved. Examples of such anon-rotational control input device include, but are not limited to, aplurality of depressible buttons (e.g., curve left, curve right, andtravel straight), a touch screen on which a driver traces or otherwiseinputs a curvature for path of travel commands, a button that istranslatable along an axis for allowing a driver to input path of travelcommands, and the like.

The trailer backup steering input apparatus 125 can be configured toprovide various feedback information to a driver of the vehicle 100.Examples of situation that such feedback information can include, butare not limited to, a status of the trailer backup assist system 105(e.g., active, in standby (e.g., when driving forward to reduce thetrailer angle), faulted, inactive, etc), that a curvature limit has beenreached (i.e., maximum commanded curvature of a path of travel of thetrailer 110), etc. To this end, the trailer backup steering inputapparatus 125 can be configured to provide a tactile feedback signal(e.g., a vibration through the knob 170) as a warning if any one of avariety of conditions occur. Examples of such conditions include, butare not limited to, the trailer 110 having jack-knifed, the trailerbackup assist system 105 has had a failure, the trailer backup assistsystem 105 or other system of the vehicle 100 has predicted a collisionon the present path of travel of the trailer 110, the trailer backupsystem 105 has restricted a commanded curvature of a trailer's path oftravel (e.g., due to excessive speed or acceleration of the vehicle100), and the like. Still further, it is disclosed that the trailerbackup steering input apparatus 125 can use illumination (e.g., an LED180) and/or an audible signal output (e.g., an audible output device185) to provide certain feedback information (e.g., notification/warningof an unacceptable trailer backup condition).

Referring now to FIGS. 2 and 3, an example of using the trailer backupsteering input apparatus 125 for dictating a curvature of a path oftravel (POT) of a trailer (i.e., the trailer 110 shown in FIG. 1) whilebacking up the trailer with a vehicle (i.e., the vehicle 100 in FIGS. 1and 2) is shown. In preparation of backing the trailer 110, the driverof the vehicle 100 drives the vehicle 100 forward along a pull-thru path(PTP) to position the vehicle 100 and trailer 110 at a first backupposition B1. In the first backup position B1, the vehicle 100 andtrailer 110 are longitudinally aligned with each other such that alongitudinal centerline axis L1 of the vehicle 100 is aligned with(e.g., parallel with or coincidental with) a longitudinal centerlineaxis 12 of the trailer 110. It is disclosed herein that such alignmentof the longitudinal axes L1, L2 at the onset of an instance of trailerbackup functionality is not a requirement for operability of a trailerbackup assist system configured in accordance with the inventive subjectmatter.

After activating the trailer backup assist system 105 (e.g., before,after, or during the pull-thru sequence), the driver begins to back thetrailer 110 by reversing the vehicle 100 from the first backup positionB1. So long as the knob 170 of the trailer backup steering inputapparatus 125 remains in the at-rest position P(AR), the trailer backupassist system 105 will steer the vehicle 100 as necessary for causingthe trailer 110 to be backed along a substantially straight path oftravel as defined by the longitudinal centerline axis L2 of the trailer110 at the time when backing of the trailer 110 began. When the trailerreaches the second backup position B2, the driver rotates the knob 170to command the trailer 110 to be steered to the right (i.e., a knobposition R(R)). Accordingly, the trailer backup assist system 105 willsteer the vehicle 100 for causing the trailer 110 to be steered to theright as a function of an amount of rotation of the knob 170 withrespect to the at-rest position P(AR), a rate movement of the knob 170,and/or a direction of movement of the knob 170 with respect to theat-rest position P(AR). Similarly, the trailer 110 can be commanded tosteer to the left by rotating the knob 170 to the left. When the trailerreaches backup position B3, the driver allows the knob 170 to return tothe at-rest position P(AR) thereby causing the trailer backup assistsystem 105 to steer the vehicle 100 as necessary for causing the trailer110 to be backed along a substantially straight path of travel asdefined by the longitudinal centerline axis L2 of the trailer 110 at thetime when the knob 170 was returned to the at-rest position P(AR).Thereafter, the trailer backup assist system 105 steers the vehicle 100as necessary for causing the trailer 110 to be backed along thissubstantially straight path to the fourth backup position 134. In thisregard, arcuate (e.g., curved) portions of a path of travel POT of thetrailer 110 are dictated by rotation of the knob 170 and straightportions of the path of travel POT are dictated by an orientation of thecenterline longitudinal axis L2 of the trailer when the knob 170 isin/returned to the at-rest position P(AR).

FIG. 4 shows a method 200 for implementing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter. In a preferred embodiment, the method 200 for implementingtrailer backup assist functionality can be carried out using the trailerbackup assist architecture discussed above in reference to the vehicle100 and trailer 110 of FIG. 1. Accordingly, trailer steering informationis provided through use of a rotational control input device (e.g., theknob 170 discussed in reference to FIG. 2).

An operation 202 is performed for receiving a trailer backup assistrequest. Examples of receiving the trailer backup assist request includeactivating the trailer backup assist system and providing confirmationthat the vehicle and trailer are ready to be backed. After receiving atrailer backup assist request (i.e., while the vehicle is beingreversed), an operation 204 is performed for receiving a trailer backupinformation signal. Examples of information carried by the trailerbackup information signal include, but is not limited to, informationfrom the trailer backup steering input apparatus 125, information fromthe hitch angle detecting apparatus 130, information from thepower-steering assist control module 135, information from the brakesystem control module 145, and information from the powertrain controlmodule 150. It is disclosed herein that information from the trailerbackup steering input apparatus 125 preferably includes trailer pathcurvature information characterizing a desired curvature for the path oftravel of the trailer, such as provided by the trailer backup steeringinput apparatus 125 discussed above in reference to FIGS. 1 and 2. Inthis manner, the operation 204 for receiving the trailer backupinformation signal can include receiving trailer path curvatureinformation characterizing the desired curvature for the path of travelof the trailer.

If the trailer backup information signal indicates that a change incurvature of the trailer's path of travel is requested (i.e., commandedvia the knob 170), an operation 206 is performed for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel. Otherwise, an operation 208 is performedfor determining vehicle steering information for maintaining a currentstraight-line heading of the trailer (i.e., as defined by thelongitudinal centerline axis of the trailer). Thereafter, an operation210 is performed for providing the vehicle steering information to apower-steering assist system of the vehicle, followed by an operation212 being performed for determining the trailer backup assist status. Ifit is determined that trailer backup is complete, an operation 214 isperformed for ending the current trailer backup assist instance.Otherwise the method 200 returns to the operation 204 for receivingtrailer backup information. Preferably, the operation for receiving thetrailer backup information signal, determining the vehicle steeringinformation, providing the vehicle steering information, and determiningthe trailer backup assist status are performed in a monitoring fashion(e.g., at a high rate of speed of a digital data processing device).Accordingly, unless it is determined that reversing of the vehicle forbacking the trailer is completed (e.g., due to the vehicle having beensuccessfully backed to a desired location during a trailer backup assistinstance, the vehicle having to be pulled forward to begin anothertrailer backup assist instance, etc), the method 200 will continually beperforming the operations for receiving the trailer backup informationsignal, determining the vehicle steering information, providing thevehicle steering information, and determining the trailer backup assiststatus.

It is disclosed herein that the operation 206 for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel preferably includes determining vehiclesteering information as a function of trailer path curvature informationcontained within the trailer backup information signal. As will bediscussed below in greater detail, determining vehicle steeringinformation can be accomplished through a low order kinematic modeldefined by the vehicle and the trailer. Through such a model, arelationship between the trailer path curvature and commanded steeringangles of steered wheels of the vehicle can be generated for determiningsteering angle changes of the steered wheels for achieving a specifiedtrailer path curvature. In this manner, the operation 206 fordetermining vehicle steering information can be configured forgenerating information necessary for providing trailer path curvaturecontrol in accordance with the inventive subject matter.

In some embodiments of the inventive subject matter, the operation 210for providing the vehicle steering information to the power-steeringassist system of the vehicle causes the steering system to generate acorresponding steering command as a function of the vehicle steeringinformation. The steering command is interpretable by the steeringsystem and is configured for causing the steering system to move steeredwheels of the steering system for achieving a steered angle as specifiedby the vehicle steering information. Alternatively, the steering commandcan be generated by a controller, module or computer external to thesteering system (e.g., a trailer backup assist control module) and beprovided to the steering system.

In parallel with performing the operations for receiving the trailerbackup information signal, determining the vehicle steering information,providing the vehicle steering information, and determining the trailerbackup assist status, the method 200 performs an operation 216 formonitoring the trailer backup information for determining if anunacceptable trailer backup condition exists. Examples of suchmonitoring include, but are not limited to assessing a hitch angle todetermine if a hitch angle threshold is exceeded, assessing a backupspeed to determine if a backup speed threshold is exceeded, assessingvehicle steering angle to determine if a vehicle steering anglethreshold is exceeded, assessing other operating parameters (e.g.,vehicle longitudinal acceleration, throttle pedal demand rate and hitchangle rate) for determining if a respective threshold value is exceeded,and the like. Backup speed can be determined from wheel speedinformation obtained from one or more wheel speed sensors of thevehicle. If it is determined that an unacceptable trailer backupcondition exists, an operation 218 is performed for causing the currentpath of travel of the trailer to be inhibited (e.g., stopping motion ofthe vehicle), followed by the operation 214 being performed for endingthe current trailer backup assist instance. It is disclosed herein thatprior to and/or in conjunction with causing the current trailer path tobe inhibited, one or more actions (e.g., operations) can be implementedfor providing the driver with feedback (e.g., a warning) that such anunacceptable trailer angle condition is impending or approaching. In oneexample, if such feedback results in the unacceptable trailer anglecondition being remedied prior to achieving a critical condition, themethod can continue with providing trailer backup assist functionalityin accordance with operations 204-212. Otherwise, the method can proceedto operation 214 for ending the current trailer backup assist instance.In conjunction with performing the operation 214 for ending the currenttrailer backup assist instance, an operation can be performed forcontrolling movement of the vehicle to correct or limit a jackknifecondition (e.g., steering the vehicle, decelerating the vehicle,limiting magnitude and/or rate of driver requested trailer curvatureinput, and/or the like to preclude the hitch angle from being exceeded).

Turning now to a discussion of a kinematic model used to calculate arelationship between a curvature of a path of travel of a trailer andthe steering angle of a vehicle towing the trailer, a low orderkinematic model can be desirable for a trailer back-up assist systemconfigured in accordance with some embodiments of the inventive subjectmatter. To achieve such a low order kinematic model, certain assumptionsare made with regard to parameters associated with the vehicle/trailersystem. Examples of such assumptions include, but are not limited to,the trailer being backed by the vehicle at a relatively low speed,wheels of the vehicle and the trailer having negligible (e.g., no) slip,tires of the vehicle, vehicle lateral compliance, and the trailer havingnegligible (e.g., no) deformation, actuator dynamics of the vehiclebeing negligible, the vehicle and the trailer exhibiting negligible(e.g., no) roll or pitch motions.

As shown in FIG. 5, for a system defined by a vehicle 302 and a trailer304, the kinematic model 300 is based on various parameters associatedwith the vehicle 302 and the trailer 304. These kinematic modelparameters include:

-   -   δ: steering angle at steered front wheels 306 of the vehicle        302;    -   α: yaw angle of the vehicle 302;    -   β: yaw angle of the trailer 304;    -   γ: hitch angle (γ=β−α);    -   W: wheel base of the vehicle 302;    -   L: length between hitch point 308 and rear axle 310 of the        vehicle 302;    -   D: length between hitch point 308 and axle 312 of the trailer        304; and    -   r₂: curvature radius for the trailer 304.

The kinematic model 300 of FIG. 5 reveals a relationship between trailerpath radius of curvature r₂ at the midpoint 314 of an axle 306 of thetrailer 304, steering angle δ of the steered wheels 306 of the vehicle302, and the hitch angle γ. As shown in the equation below, thisrelationship can be expressed to provide the trailer path curvature κ₂such that, if γ is given, the trailer path curvature κ₂ can becontrolled based on regulating the steering angle δ (where β(.) istrailer yaw rate and η(.) is trailer velocity).

$\begin{matrix}{\kappa_{2} = \frac{1}{r_{2}}} \\{= \frac{\overset{.}{\beta}}{\overset{.}{\eta}}} \\{= \frac{{\left( {W + \frac{{KV}^{2}}{g}} \right)\sin\;\gamma} + {L\;\cos\;\gamma\;\tan\;\delta}}{D\left( {{\left( {W + \frac{{KV}^{2}}{g}} \right)\cos\;\gamma} - {L\;\sin\;\gamma\;\tan\;\delta}} \right)}}\end{matrix}$

Or, this relationship can be expressed to provide the steering angle δas a function of trailer path curvature κ₂ and hitch angle γ.

$\begin{matrix}{\delta = {\tan^{- 1}\left( \frac{\left( {W + \frac{{KV}^{2}}{g}} \right)\left\lbrack {{\kappa_{2}D\;\cos\;\gamma} - {\sin\;\gamma}} \right\rbrack}{{{DL}\;\kappa_{2}\sin\;\gamma} + {L\;\cos\;\gamma}} \right)}} \\{= {F\left( {\gamma,\kappa_{2},K} \right)}}\end{matrix}$

Accordingly, for a particular vehicle and trailer combination, certainkinematic model parameters (e.g., D, W and L) are constant and assumedknown. V is the vehicle longitudinal speed and g is the acceleration dueto gravity. K is a speed dependent parameter which when set to zeromakes the calculation of steering angle independent of vehicle speed.For example, vehicle-specific kinematic model parameters can bepredefined in an electronic control system of a vehicle andtrailer-specific kinematic model parameters can be inputted by a driverof the vehicle. Trailer path curvature κ₂ is determined from the driverinput via a trailer backup steering input apparatus. Through the use ofthe equation for providing steering angle, a corresponding steeringcommand can be generated for controlling a steering system (e.g., anactuator thereof) of the vehicle.

FIG. 6 shows an example of a trailer path curvature function plot 400for a rotary-type trailer backup steering input apparatus (e.g., thetrailer backup steering input apparatus 125 discussed above in referenceto FIGS. 1 and 2). A value representing trailer path curvature (e.g.,trailer path curvature κ2) is provided as an output signal from therotary-type trailer backup steering input apparatus as a function ofuser input movement. In this example, a curve 402 specifying trailerpath curvature relative to user input (e.g., amount of rotation) at arotary input device (e.g., a knob) is defined by a cubic function.However, a skilled person will appreciate that embodiments of theinventive subject matter are not limited to any particular functionbetween a magnitude and/or rate of input at a trailer backup steeringinput apparatus (e.g., knob rotation) and a resulting trailer pathcurvature value.

Referring to FIG. 5, in preferred embodiments of the inventive subjectmatter, it is desirable to limit the potential for the vehicle 302 andthe trailer 304 to attain a jackknife angle (i.e., the vehicle/trailersystem achieving a jackknife condition). A jackknife angle γ(j) refersto a hitch angle γ that cannot be overcome by the maximum steering inputfor a vehicle, when the vehicle is reversing, such as, for example, thesteered front wheels 306 of the vehicle 302 being moved to a maximumsteered angle δ at a maximum rate of steering angle change. Thejackknife angle γ(j) is a function of a maximum wheel angle for thesteered wheel 306 of the vehicle 302, the wheel base W of the vehicle302, the distance L between hitch point 308 and the rear axle 310 of thevehicle 302, and the length D between the hitch point 308 and the axle312 of the trailer 304. When the hitch angle γ for the vehicle 302 andthe trailer 304 achieves or exceeds the jackknife angle γ(j), thevehicle 302 must be pulled forward to reduce the hitch angle γ. Thus,for limiting the potential for a vehicle/trailer system attaining ajackknife angle, it is preferable to control the yaw angle of thetrailer while keeping the hitch angle of the vehicle/trailer systemrelatively small.

Referring to FIGS. 5 and 7, a steering angle limit for the steered frontwheels 306 requires that the hitch angle γ cannot exceed the jackknifeangle γ(j), which is also referred to as a critical hitch angle. Thus,under the limitation that the hitch angle γ cannot exceed the jackknifeangle γ(j), the jackknife angle γ(j) is the hitch angle γ that maintainsa circular motion for the vehicle/trailer system when the steered wheels306 are at a maximum steering angle δ(max). The steering angle forcircular motion with hitch angle is defined by the following equation.

${\tan\;\delta_{\max}} = \frac{W\;\sin\;\gamma_{\max}}{D + {L\;\cos\;\gamma_{\max}}}$

Solving the above equation for hitch angle allows jackknife angle γ(j)to be determined. This solution, which is shown in the followingequation, can be used in implementing trailer backup assistfunctionality in accordance with the inventive subject matter formonitoring hitch angle in relation to jackknife angle.

${{\cos\;\overset{\_}{\gamma}} = \frac{{- b} \pm \sqrt{b^{2} - {4\;{ac}}}}{2\; a}},$

where,

-   -   a=L² tan² δ(max)+W;    -   b=2 LD tan² δ(max); and    -   c=D² tan² δ(max)−W².

In certain instances of backing a trailer, a jackknife enablingcondition can arise based on current operating parameters of a vehiclein combination with a corresponding hitch angle. This condition can beindicated when one or more specified vehicle operating thresholds aremet while a particular hitch angle is present. For example, although theparticular hitch angle is not currently at the jackknife angle for thevehicle and attached trailer, certain vehicle operating parameters canlead to a rapid (e.g., uncontrolled) transition of the hitch angle tothe jackknife angle for a current commanded trailer path curvatureand/or can reduce an ability to steer the trailer away from thejackknife angle. One reason for a jackknife enabling condition is thattrailer curvature control mechanisms (e.g., those in accordance with theinventive subject matter) generally calculate steering commands at aninstantaneous point in time during backing of a trailer. However, thesecalculations will typically not account for lag in the steering controlsystem of the vehicle (e.g., lag in a steering EPAS controller). Anotherreason for the jackknife enabling condition is that trailer curvaturecontrol mechanisms generally exhibit reduced steering sensitivity and/oreffectiveness when the vehicle is at relatively high speeds and/or whenundergoing relatively high acceleration.

FIG. 8 shows a method 500 for implementing jackknife countermeasuresfunctionality in accordance with an embodiment of the inventive subjectmatter for a vehicle and attached trailer. Trailer backup assistfunctionality in accordance with the inventive subject matter caninclude jackknife countermeasures functionality. Alternatively,jackknife countermeasures functionality in accordance with an embodimentof the inventive subject matter can be implemented separately from otheraspects of trailer backup assist functionality.

The method 500 begins when operation 502 is performed for receivingjackknife determining information characterizing a jackknife enablingcondition of the vehicle-trailer combination at a particular point intime (e.g., at the point in time when the jackknife determininginformation was sampled). Examples of the jackknife determininginformation includes, but are not limited to, information characterizinga hitch angle, information characterizing a vehicle accelerator pedaltransient state, information characterizing a speed of the vehicle,information characterizing longitudinal acceleration of the vehicle,information characterizing a brake torque being applied by a brakesystem of the vehicle, information characterizing a powertrain torquebeing applied to driven wheels of the vehicle, and informationcharacterizing the magnitude and rate of driver requested trailercurvature. The operation 502 for receiving jackknife determininginformation can be the first operation in a sampling process wherejackknife determining information is sampled upon initiation of aninstance of implementing jackknife countermeasures functionality. Inthis regard, jackknife determining information would be continuallymonitored such as, for example, by a electronic control unit (ECU) thatcarries out trailer backup assist (TBA) functionality. As discussedabove in reference to FIG. 5, a kinematic model representation of thevehicle and the trailer can be used to determine a jackknife angle forthe vehicle-trailer combination. However, the inventive subject matteris not unnecessarily limited to any specific approach for determiningthe jackknife angle.

After receiving the jackknife determining information, an operation 504is performed for assessing the jackknife determining information fordetermining if the vehicle-trailer combination attained the jackknifeenabling condition at the particular point in time. The objective of theoperation 504 for assessing the jackknife determining information isdetermining if a jackknife enabling condition has been attained at thepoint in time defined by the jackknife determining information. If it isdetermined that a jackknife enabling condition is not present at theparticular point in time, the method 500 returns to the operation 502for receiving another instance of the jackknife determining information.If it is determined that a jackknife enabling condition is present atthe particular point in time, an operation 506 is performed fordetermining an applicable counter-measure or counter-measures toimplement. Accordingly, in some embodiments of the inventive subjectmatter, an applicable counter-measure will be selected dependent upon aparameter identified as being a key influencer of the jackknife enablingcondition. However, in other embodiments, an applicable counter-measurewill be selected as being most able to readily alleviate the jackknifeenabling condition. In still other embodiment, a pre-definedcounter-measure or pre-defined set of counter-measures may be theapplicable counter-measure(s).

The objective of a counter-measure in the context of the inventivesubject matter (i.e., a jackknife reduction countermeasure) is toalleviate a jackknife enabling condition. To this end, such acounter-measure can be configured to alleviate the jackknife enablingcondition using a variety of different strategies. In a vehicle speedsensitive counter-measure strategy, actions taken for alleviating thejackknife enabling condition can include overriding and/or limitingdriver requested trailer radius of curvature (e.g., being requested viaa trailer backup steering input apparatus configured in accordance withthe inventive subject matter) as a function of vehicle speed (e.g., viaa look-up table correlating radius of curvature limits to vehicle speedas shown in FIG. 6). In a counter-measure strategy where trailercurvature requests are limited as a function of speed and drivercurvature command transient rates, actions taken for alleviating thejackknife enabling condition can include rate limiting trailer curvaturecommand transients as requested by a driver above a pre-defined vehiclespeed whereas, under the pre-defined vehicle speed, the as-requestedtrailer curvature are not rate limited. In a torque limitingcounter-measure strategy, actions taken for alleviating the jackknifeenabling condition can include application of full available powertraintorque being inhibited when the jackknife enabling condition is presentwhile the vehicle is above a pre-defined speed and application of fullavailable powertrain torque being allowed when the vehicle speed isreduced below the pre-defined speed while in the torque inhibiting mode.As opposed to a fixed pre-defined speed, the torque limitingcounter-measure strategy can utilize a speed threshold that is afunction of hitch angle (i.e., speed threshold inversely proportional tohitch angle acuteness). In a driver accelerator pedal transientdetection counter-measure strategy, actions taken for alleviating thejackknife enabling condition can include overriding and/or limitingdriver requested trailer radius of curvature as a function of transientaccelerator pedal requests (e.g., requested trailer radius of curvaturelimited when a large accelerator pedal transient is detected). In ahitch angle rate sensitive counter-measure strategy, actions taken foralleviating the jackknife enabling condition can include using hitchangle rate in a predefined or calculated mapping with current hitchangle position to limit driver requested trailer radius of curvature.Accordingly, in view of the disclosures made herein, a skilled personwill appreciate that embodiments of the inventive subject matter are notunnecessarily limited to a counter-measure strategy of any particularconfiguration.

As disclosed above, implementation of trailer backup assistfunctionality in accordance with the inventive subject matter canutilize a kinematic model for determining steering control information,jackknife enabling conditions, and jackknife angle. Such a kinematicmodel has many parameters than can influence trailer curvature controleffectiveness. Examples of these parameters include, but are not limitedto, the vehicle wheelbase, understeer gradient gain, vehicle trackwidth, maximum steer angle at the vehicle front wheels, minimum turningradius of vehicle, maximum steering rate able to be commanded by thesteering system, hitch ball to trailer axle length, and vehicle rearaxle to hitch ball length. Sensitivity analysis for a given kinematicmodel can be used to provide an understanding (e.g., sensitivity) of therelationships between such parameters, thereby providing informationnecessary for improving curvature control performance and for reducingthe potential for jackknife enabling conditions. For example, through anunderstanding of the sensitivity of the parameters of a kinematic model,scaling factors can be used with speed dependent jackknifecounter-measures to reduce jackknife potential (e.g., for specialapplications such as short wheelbase conditions).

Still referring to FIG. 8, after determining the applicablecountermeasure(s), an operation 508 is performed for implementing thechosen jackknife countermeasure(s) and an operation 510 is performed forinitiating a jackknife warning. As discussed above in regard tocounter-measure strategies, implementing the jackknifecounter-measure(s) can include commanding a speed controlling system ofthe vehicle to transition to an altered state of operation in which aspeed of the vehicle is reduced, commanding the steering control systemof the vehicle to transition to an altered state of operation in which aradius of a curvature of a path of the trailer is increased, command thesteering control system of the vehicle to transition to an altered stateof operation in which an increase in the radius of the curvature of thepath of the trailer is inhibited, commanding a brake control system ofthe vehicle to apply brake torque to reduce vehicle speed/inhibitvehicle acceleration, and/or commanding a powertrain control system ofthe vehicle to inhibit full available powertrain torque from beingdelivered to driven wheels of the vehicle until another jackknifeenabling parameter (e.g. vehicle speed) is below a defined threshold. Incertain embodiments of the inventive subject matter, the jackknifewarning is provided to the driver using at least one vehicle controlsystem through which the jackknife counter-measure is implemented. Speedreduction can be accomplished by any number of means such as, forexample, limiting throttle inputs (e.g., via a terrain managementfeature) and/or transitioning a transmission to a reverse low gear ifthe vehicle is equipped with a multi-range reverse gear transmission.Examples of such system-specific warning approach include, but are notlimited to, providing a warning through an accelerator pedal of thevehicle (e.g., via haptic feedback) if the counter-measure includeslimiting speed of the vehicle and/or providing a warning through aninput element (e.g., knob) of a trailer backup steering input apparatusof the vehicle (e.g., via haptic feedback if the counter-measureincludes limiting driver requested trailer radius of curvature), throughhaptic seat vibration warning, through a visual warning (e.g., through avisual display apparatus of the towing vehicle) and/or through audiblewarnings (e.g., through an audio output apparatus of the towingvehicle), or the like. One embodiment of utilizing warnings relating tovehicle speed as it related to onset or presence of a jackknife enablingcondition includes implementation of a dual stage warning. For example,when a backing speed of the vehicle increases sufficiently for causing aspeed of the vehicle to reach a lower (i.e., first) speed thresholdduring backing of the trailer, a driver of the vehicle would be providedwith a first warning indication (e.g., via haptic, audible, and/orvisual means as implemented by the trailer backup assist system) forinforming the driver that there is the need to reduce the speed of thevehicle to alleviate or prelude the jackknife enabling condition. If thedriver does not correspondingly respond by causing a speed of thevehicle to be reduced (or not to further increase) and the vehiclecontinues to gain speed such that it passes a higher (i.e. a second)speed threshold, the driver of the vehicle would be provided with asecond warning indication (e.g., a more severed haptic, audible, and/orvisual means as implemented by the trailer backup assist system) forinforming the driver that there is an immediate need to reduce the speedof the vehicle to alleviate or prelude the jackknife enabling condition.The first and/or the second speed indication warnings can be implementedin conjunction with a respective speed limiting counter-measure measures(e.g., the trailer backup assist system causing activation of a brakesystem of the vehicle and/or reducing a throttle position of thevehicle).

Referring now to instructions processable by a data processing device,it will be understood from the disclosures made herein that methods,processes and/or operations adapted for carrying out trailer backupassist functionality as disclosed herein are tangibly embodied bynon-transitory computer readable medium having instructions thereon thatare configured for carrying out such functionality. The instructions aretangibly embodied for carrying out the method 200 disclosed anddiscussed above and can be further configured for limiting the potentialfor a jackknife condition such as, for example, by monitoring jackknifeangle through use of the equations discussed in reference to FIGS. 5 and7 and/or by implementing jackknife countermeasures functionalitydiscussed above in reference to FIG. 8. The instructions may beaccessible by one or more data processing devices from a memoryapparatus (e.g. RAM, ROM, virtual memory, hard drive memory, etc), froman apparatus readable by a drive unit of a data processing system (e.g.,a diskette, a compact disk, a tape cartridge, etc) or both. Accordingly,embodiments of computer readable medium in accordance with the inventivesubject matter include a compact disk, a hard drive, RAM or other typeof storage apparatus that has imaged thereon a computer program (i.e.,instructions) configured for carrying out trailer backup assistfunctionality in accordance with the inventive subject matter.

In a preferred embodiment of the inventive subject matter, a trailerback-up assist control module (e.g., the trailer back-up assist controlmodule 120 discussed above in reference to FIG. 1) comprises such a dataprocessing device, such a non-transitory computer readable medium, andsuch instructions on the computer readable medium for carrying outtrailer backup assist functionality (e.g., in accordance with the method200 discussed above in reference to FIG. 2 and/or the method 500discussed above in reference to FIG. 8). To this end, the trailerback-up assist control module can comprise various signal interfaces forreceiving and outputting signals. For example, a jackknife enablingcondition detector can include a device providing hitch angleinformation and hitch angle calculating logic of the trailer back-upassist control module. A trailer back-up assist control module in thecontext of the inventive subject matter can be any control module of anelectronic control system that provides for trailer back-up assistcontrol functionality in accordance with the inventive subject matter.Furthermore, it is disclosed herein that such a control functionalitycan be implemented within a standalone control module (physically andlogically) or can be implemented logically within two or more separatebut interconnected control modules (e.g., of an electronic controlsystem of a vehicle) In one example, trailer back-up assist controlmodule in accordance with the inventive subject matter is implementedwithin a standalone controller unit that provides only trailer backupassist functionality. In another example, trailer backup assistfunctionality in accordance with the inventive subject matter isimplemented within a standalone controller unit of an electronic controlsystem of a vehicle that provides trailer backup assist functionality aswell as one or more other types of system control functionality of avehicle (e.g., anti-lock brake system functionality, steering powerassist functionality, etc). In still another example, trailer backupassist functionality in accordance with the inventive subject matter isimplemented logically in a distributed manner whereby a plurality ofcontrol units, control modules, computers, or the like (e.g., anelectronic control system) jointly carry out operations for providingsuch trailer backup assist functionality.

In the preceding detailed description, reference has been made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments in which the inventive subjectmatter may be practiced. These embodiments, and certain variantsthereof, have been described in sufficient detail to enable thoseskilled in the art to practice embodiments of the inventive subjectmatter. It is to be understood that other suitable embodiments may beutilized and that logical, mechanical, chemical and electrical changesmay be made without departing from the spirit or scope of such inventivedisclosures. To avoid unnecessary detail, the description omits certaininformation known to those skilled in the art. The preceding detaileddescription is, therefore, not intended to be limited to the specificforms set forth herein, but on the contrary, it is intended to coversuch alternatives, modifications, and equivalents, as can be reasonablyincluded within the spirit and scope of the appended claims.

What is claimed is:
 1. A method for preventing a jackknife between a vehicle having a controller and a trailer towed by the vehicle, comprising the steps of: implementing a trailer path curvature command for a reversing path of travel of the trailer during backing of the trailer, the trailer path curvature command is relative to a zero curvature command position that is defined by backward movement of the trailer along a substantially straight path defined by a centerline longitudinal axis of the trailer; determining a jackknife threshold based on kinematics of the trailer and the vehicle; detecting an imminent jackknife condition of the reversing, path based on jackknife information and the jackknife threshold; and implementing as jackknife counter-measure in response to the imminent jackknife condition by altering an operating parameter of the vehicle.
 2. The method of claim 1, further comprising initiating a jackknife warning to a driver of the vehicle in response to detecting the imminent jackknife condition, the jackknife warning is provided to the driver using at least one vehicle control system.
 3. The method of claim 1 wherein implementing the jackknife counter-measure includes at least one of reducing a speed of the vehicle, increasing a radius of a curvature of the reversing path of the trailer, and inhibiting a decrease in the radius of the curvature of the reversing path of the trailer.
 4. The method of claim 1 wherein implementing the jackknife counter-measure includes restricting powertrain torque to driven wheels of the vehicle.
 5. The method of claim 1 wherein the imminent jackknife condition is detected based on an accelerator pedal transient value, a hitch angle value, a hitch angle rate, vehicle velocity, vehicle acceleration, trailer yaw rate and a trailer path curvature value.
 6. The method of claim 1 wherein the imminent jackknife condition is detected when the jackknife threshold is met and the jackknife threshold is met when an accelerator pedal transient value, a hitch angle value, a hitch angle rate, vehicle velocity, vehicle acceleration, trailer yaw rate and a trailer path curvature value simultaneously meet respective threshold values.
 7. The method of claim 1 wherein the jackknife information includes a vehicle speed value and a trailer path curvature value, the jackknife threshold is met when the vehicle speed value and the trailer path curvature value simultaneously meet respective threshold values.
 8. The method of claim 7 wherein implementing the jackknife counter-measure includes reducing to speed of the vehicle by restricting powertrain torque to driven wheels of the vehicle.
 9. A trailer backup control system for a vehicle towing a trailer, comprising: an input apparatus for providing a trailer path curvature signal approximating a desired curvature for a reverse path of travel of the trailer relative to a zero curvature position for backward movement of the trailer in a straight path defined by a centerline longitudinal axis of the trailer; a trailer angle sensor for sensing a hitch angle between the vehicle and the trailer; and a trailer backup assist controller determining vehicle steering information based on the trailer path curvature signal and the hitch angle and the trailer backup assist controller altering a vehicle operating parameter when a jackknife condition is imminent.
 10. The system of claim 9 further comprising a power assist steering system of the vehicle for steering steered wheels of the vehicle as a function of the vehicle steering information.
 11. The system of claim 9, wherein the jackknife condition is imminent when a jackknife threshold is met, the jackknife threshold includes a hitch angle threshold and a hitch angle rate threshold.
 12. The system of claim 9, wherein altering the vehicle operating parameter includes at least one of decreasing a position of a throttle of the vehicle and actuating a brake system of the vehicle.
 13. The system of claim 9, wherein altering the vehicle operating parameter includes increasing a radius of curvature of a reversing path of the trailer by steering the steered wheels of the vehicle.
 14. The system of claim 9 further comprising a warning device that initiates a warning to a driver of the vehicle when the jackknife condition is imminent.
 15. A method for preventing a jackknife between a vehicle having a controller and a trailer, the method comprising the steps of: implementing a vehicle steering command generated from to driver input desired curvature for a reverse path of travel of the trailer during hacking of the trailer by the vehicle, the desired curvature is relative to a zero curvature command position that is defined by backward movement of the trailer along a substantially straight path defined by a centerline: longitudinal axis of the trailer; sensing a hitch angle between the vehicle and the trailer; determining a jackknife threshold for reversing the trailer based on kinematics of the vehicle and the trailer; detecting an imminent jackknife condition during backing of the trailer based on the hitch angle and the jackknife threshold; and altering an operating parameter of the vehicle in response to detecting the imminent jackknife condition.
 16. The method of claim 15 wherein the step of altering an operating parameter of the vehicle includes one of reducing a speed of the vehicle, increasing a radius of curvature of the reversing path of the trailer, and inhibiting as decrease in the radius of curvature of the reversing path of the trailer.
 17. The method of claim 16 wherein reducing the speed of the vehicle further comprises restricting powertrain torque of the vehicle.
 18. The method of claim 15 further comprising the steps of: issuing a first jackknife warning in response to a first speed threshold being reached by the vehicle during backing of the trailer; and issuing a second jackknife warning in response to a speed of the vehicle increasing by a defined amount after the first jackknife warning is issued.
 19. The method of claim 15 wherein the jackknife condition is detected when a vehicle speed value and a trailer path curvature value simultaneously meet respective threshold values. 